Objective: To study the clinical and electroretinographic findings of affected males and female carriers in a family with X-linked cone-rod dystrophy (COD-1).
Design: Observational case series.
Participants: Twenty-five members of a five-generation pedigree were examined.
Methods: A history of visual impairment including age at onset, loss of acuity, color vision abnormalities, photophobia, and nyctalopia was obtained. A complete ophthalmologic examination was performed, including kinetic perimetry with a Goldmann perimeter, FM 100-hue testing, and standardized Ganzfeld electroretinography following the ISCEV protocol.
Main outcome measures: Patients were classified as affected or unaffected on the basis of the clinical examination. All carrier females had affected sons.
Results: Nine affected males and seven female carriers were identified. Affected males noted decreased visual acuity and poor color vision within the first two decades of life. Early in the disease, macular retinal pigment epithelial (RPE) changes were found that progressed to an atrophic macular scar by the fifth decade. Evidence of progression from macular pigment mottling to an atrophic macular lesion over a 13-year period was identified in one patient. The photopic, single-flash, b-wave amplitude was low in all affected males and declined with age. The 30-Hz flicker b-wave implicit times were abnormally prolonged in all affected males. Female carriers were asymptomatic although three had slightly abnormal color vision and small paracentral field defects and subtle RPE defects were found in three carriers. Carriers demonstrated prolongation of the 30-Hz flicker b-wave implicit time and interocular asymmetry. Five of seven carriers and two affected males demonstrated reduced oscillatory potentials and an abnormal-appearing flattened photopic a-wave. Five men and two women demonstrated a characteristic tapetal-like retinal sheen.
Conclusions: Affected patients in this pedigree demonstrate early loss of visual acuity and poor cone function with late rod involvement. Female carriers may appear clinically normal or may be identified by subtle color vision defects, fundus abnormalities, prolongation of the 30-Hz flicker implicit time with interocular asymmetry, or an abnormal flattened photopic a-wave. Genetic linkage analysis of this family was recently reported and the disease-causing gene has been mapped to an approximately 1-Mb interval on chromosome Xp11.4.